factor out solc JSON interface crate (#264)

The differential testing framework will make a second consumer. There
seems to be no re-usable Rust crate for this. But we already have
everything here, just needs a small refactor to make it fully re-usable.

- Mostly decouple the solc JSON-input-output interface types from the
`solidity` frontend crate
- Expose the JSON-input-output interface types in a dedicated crate

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/solidity/src/build/contract.rs

@@ -5,12 +5,11 @@ use std::fs::File;
 use std::io::Write;
 use std::path::Path;
 
+use revive_solc_json_interface::CombinedJsonContract;
+use revive_solc_json_interface::SolcStandardJsonOutputContract;
 use serde::Deserialize;
 use serde::Serialize;
 
-use crate::solc::combined_json::contract::Contract as CombinedJsonContract;
-use crate::solc::standard_json::output::contract::Contract as StandardJsonOutputContract;
-
 /// The Solidity contract build.
 #[derive(Debug, Serialize, Deserialize)]
 pub struct Contract {
@@ -131,7 +130,7 @@ impl Contract {
     /// Writes the contract text assembly and bytecode to the standard JSON.
     pub fn write_to_standard_json(
         self,
-        standard_json_contract: &mut StandardJsonOutputContract,
+        standard_json_contract: &mut SolcStandardJsonOutputContract,
     ) -> anyhow::Result<()> {
         standard_json_contract.metadata = Some(self.metadata_json);